In the real-time service, application characteristics, for example, characteristics of VoIP (Voice over Internet Protocol) or the like is mapped to each radio bearer (RB), as a QoS-related attribute. Accordingly, it is assumed that an estimation of the application type is not performed in the MAC layer.
HSDPA (High Speed Downlink Packet Access) is configured such that, at each TTI (Transmission Time Interval) via an HS-SCCH (High speed-Shared Control Channel), a mobile station is notified of an assignment of a transmission opportunity to the downlink data that is addressed to the mobile station. More specifically, in the HSDPA, the HS-SCCH is transmitted before the downlink data is transmitted, so that a mobile station is notified of assignment information (scheduling information) for the downlink data in advance. The mobile station that detects that a transmission opportunity is assigned to the downlink data addressed to the own mobile station performs a decoding process for the downlink data, based on the assignment information (the scheduling information) for the downlink data.
However, the data is transmitted, for example, once in every tens ms in a characteristic traffic such as a voice traffic. Accordingly, when a configuration is employed in which the assignment of the transmission opportunity to the data is notified via a channel equivalent to the HS-SCCH, overhead of a signaling channel is made too large to achieve efficiency.
In this regard, in standardization of evolved UTRA, “persistent scheduling” is proposed, in which the transmission opportunity is assigned to the data to be used for the application, based on a predetermined period according to the characteristics of the application.
For example, in the “persistent scheduling”, as an attribute of a radio bearer, “whether or not the persistent scheduling can be applied (assignment period)” is set.
Here, the assignment period can be set in a frame unit (N×10 msec: N is an integer of N>0). When the assignment period is “0,” “persistent scheduling” is not applied.
In the “evolved UTRA,” when data having a known traffic pattern (such as VoIP or the like) is transmitted and when the assignment information (scheduling information) for the downlink data is transmitted via a signaling channel equivalent to the HS-SCCH in the HSDPA, overhead of the signaling channel is increased.
In addition, in the “evolved UTRA,” when the number of users (mobile stations) using the VoIP is increased, the overhead of the signaling channel is relatively increased. Accordingly, a system capacity may be consumed.
For this reason, as described above, there has been proposed “persistent scheduling”. In the persistent scheduling, the transmission frequency of the scheduling information transmitted via the signaling channel equivalent to the HS-SCCH in the HSDPA can be reduced, when the data having a known traffic pattern (such as VoIP or the like) is transmitted. There has been also proposed combined use of the “persistent scheduling” and “normal scheduling”. In the normal scheduling, the transmission opportunity is assigned, at each TTI, to the data addressed to a user (mobile station) having a favorable radio channel condition.
However, the above-described background art has the following problems.
It can be considered a case where a reception quality in an L1/L2 control channel equivalent to the HS-SCCH in the HSDPA is temporarily deteriorated greatly owing to such as a shadowing, a high-speed movement, or the like. In this case, the mobile station cannot receive the assignment information (scheduling information) for the data to be transmitted via the L1/L2 control channel, even when data addressed to the own mobile station exists.
In addition, in a system to which a next generation system “UTRA-UTRAN LTE (Long Term Evolution)” is applied, it is assumed that a plurality of symbols from the beginning of one sub-frame is assigned for the L1/L2 control channel. However, a radio resource that can be assigned to the L1/L2 control channel is limited. Accordingly, the reception quality in the L1/L2 control channel cannot be improved sufficiently.
Meanwhile, in a case of a data channel, an error resilience can be enhanced by changing a coding ratio of the data to be transmitted, and, for example, by coding the data at a low coding ratio. In addition, in the case of the data channel, by repeatedly transmitting the data, the flexibility of using a method for improving the reception quality can be increased compared with the case of the L1/L2 control channel.
For this reason, even when the scheduling information (for example, assignment information for data) transmitted via the L1/L2 control channel cannot be received, the data transmitted via the data channel may be received.